ES336560A1 - Condition responsive electric switch mechanism - Google Patents

Abstract

In a temperature responsive switch a temperature sensitive element 30, Fig. 3, contains a partially saturated vapour region and liquid region at the operating temperature range whereby heat transfer takes place within the element 30 during snap-action of the contacts and thermal damping of the switch actuator is obtained to reduce the noise of operation. A bias heater 144 is arranged on the expansible chamber 34 to maintain the chamber at a higher temperature so that the liquid region 39c for heat transfer is always maintained at the heat sensitive end 139. The expansible chamber 34 acts against an adjustable threaded stud 108 in a carrier 109 loaded by coil spring 20a and actuates the switch contact 12 through a pivoted actuating lever 13 and push rod 95. A toggle spring 40 arranged between the actuator 13 and adjusting screw 47 is arranged to override the action of spring 20 and provides a negative spring characteristic to snap the contact 12 open. The bias heater 144 is maintained permanently in circuit but a second pre-heater 140 is arranged between the capsule 34 and the sensitive end 139 and is connected in parallel with the load heater and operates to provide a contact weld-breaking action. Temperature range adjustment is provided by a control knob 28 rotating cam 26 to vary the loading on spring 20a through cam follower 25. The knob 28 also controls a manual " off " position by camming an arm 100 which depresses a pin 102 operating to hold the contacts open. In a modification, Fig. 1 (not shown), the switch actuating arm has a lost motion connection to a rigid extension of the movable con. tact spring which flexes until the rigid extension engages a fixed stop and withdraws the contact positively. In the examples the capsule is initially filled with butane at a temperature of 54 C. and gauge pressure of 60 p.s.i. in order to obtain a saturated vapour state in the operating range of (21-24 C.) at which the pressure is 17 p.s.i.